Devices and methods for measuring blood flow rate or cardiac output and for heating or cooling the body

Abstract

Heat exchanger-equipped catheters and related methods that are useable for changing or maintaining at least a portion of the body of a human or veterinary patient at a desired temperature and for the measurement of cardiac output or blood flow rate within a blood vessel, without the need for introduction of saline solution or any other foreign substance into the patient's blood.

What is claimed is: 
     
       1. A method for determining cardiac output or discerning a substantial change in cardiac output in a mammalian patient, the method comprising the steps of:
 A) providing a heat exchange catheter that comprises an elongate catheter body having a heat exchanger positioned thereon; 
 B) inserting the heat exchange catheter into the vasculature of the patient and positioning the heat exchanger within a blood vessel through which the blood flow rate is substantially the same as or bears a known relationship to cardiac output; 
 C) causing heat to be exchanged between the heat exchanger and blood flowing past the heat exchanger; 
 D) determining the amount of heat exchanged between the heat exchanger and the blood within a time period; 
 E) determining the flow rate of blood past the heat exchanger based on the amount of heat exchanged in the time period, the flow rate of blood being determined by reference to a database which correlates flow rate values to corresponding amounts of heat exchange measured in Step D for blood in vessels having different luminal diameters; and 
 F) computing at least an estimate of cardiac output or discerning a change in cardiac output, on the basis of the flow rate determined in Step E. 
 
     
     
       2. A method according to  claim 1  wherein Step C is carried out such that the amount of heat exchanged between the heat exchanger and the blood results in a change in the temperature of all or part of a patient's body so as to induce hypothermia, induce hyperthermia, maintain normothermia or achieve and maintain a temperature that is different from that patient's normothermic temperature. 
     
     
       3. A method according to  claim 1  wherein Step B comprises positioning the heat exchanger in a vessel through which venous blood flows, the venous blood flow through that vessel accounting for at least 15% of the total blood flow entering the right atrium. 
     
     
       4. A method according to  claim 1  wherein the flow rate of blood is determined in Step E by the following formula:
     CO= Heat Exchanged÷ Δt  
 
 wherein CO=the amount of blood passing through the right heart per unit time, Heat Exchanged=the amount of heat added to or removed from the blood per unit time and Δt=the difference between the temperature of the patient's blood before it undergoes heat exchange with the heat exchanger as measured by a second temperature measuring device and the temperature of blood flowing after it undergoes heat exchange with the heat exchanger through the patient's pulmonary artery as measured by a first temperature measuring device. 
 
     
     
       5. A method according to  claim 4  wherein the luminal diameter of the vessel in which the heat exchanger is positioned is estimated based on the height and weight of the patient. 
     
     
       6. A method according to  claim 4  wherein the luminal diameter of the vessel in which the heat exchanger is positioned is measured. 
     
     
       7. A method according to  claim 6  wherein the luminal diameter of the vessel in which the heat exchanger is positioned is measured on an image of the vessel obtained by an imaging technique selected from the group consisting of:
 fluoroscopy; 
 ultrasound imaging; 
 intravascular ultrasound imaging; 
 magnetic resonance imaging; 
 computed tomographic imaging; 
 angiography; and, 
 X-ray. 
 
     
     
       8. A method according to  claim 1  wherein the heat exchanger is positioned in the venous vasculature and wherein a computed or estimated cardiac output is calculated in Step F by multiplying the flow rate determined in Step E by a factor representing the portion of total venous blood flow through the right heart that comes from the vessel in which the heat exchanger is positioned. 
     
     
       9. A method according to  claim 8  wherein at least a portion of the heat exchanger is positioned in the inferior vena cave and the factor applied for that portion of the heat exchanger is approximately ⅔. 
     
     
       10. A method according to  claim 8  wherein at least a portion of the heat exchanger is positioned in the inferior vena cave and the factor applied for that portion of the heat exchanger is approximately ⅓. 
     
     
       11. A method according to  claim 8  wherein at least a portion of the heat exchanger is positioned in the right atrium and the factor applied for that portion of the heat exchanger is 100%. 
     
     
       12. A method according to  claim 9  wherein the amount of heat exchanged between the heat exchanger and the blood is determined by the formula:
     q=m· ( t   in   −t   out ) K    
 wherein q=heat exchange, m=flow rate of heat exchange fluid through the heat exchanger, t in =temperature of heat exchange fluid entering the heat exchanger, t out =temperature of heat exchange fluid exiting the heat exchanger and K=the thermal constant of the heat exchanger fluid. 
 
     
     
       13. A method according to  claim 1  wherein the catheter device provided in Step A has a heat exchanger through which a heat exchange fluid is circulated and wherein the amount of heat exchanged between the heat exchanger and the blood within a time period is calculated based on the flow rate of the heat exchange fluid, the temperature of the heat exchange fluid entering the heat exchanger and the temperature of fluid exiting the heat exchanger over the time period. 
     
     
       14. A method according to  claim 1  wherein the catheter device provided in Step A has a heat exchanger which receives power from an external power supply apparatus, and the determination of the heat exchanged between the heat exchanger and the blood is determined by measuring the power output by the power supply apparatus. 
     
     
       15. A method according to  claim 1  wherein the catheter device provided in Step A has a heat exchanger through which a heat exchange fluid is circulated and wherein the amount of heat exchanged between the heat exchanger and the blood within a time period is calculated based on the amount of power consumed by an external unit. 
     
     
       16. A method according to  claim 1  wherein the method further comprises the steps of:
 measuring the temperature of blood downstream of the heat exchanger; 
 measuring the temperature of blood upstream of the heat exchanger; and, wherein, 
 the amount of heat exchanged in the time period is determined in Step D by the formula:
   downstream temperature−upstream temperature.
 
 
 
     
     
       17. A method according to  claim 16  wherein the temperature of blood upstream of the heat exchanger is taken as the temperature of the patient's body taken at an extravascular location. 
     
     
       18. A method according to  claim 16  wherein the temperature of blood downstream of the heat exchanger is measured in the pulmonary artery. 
     
     
       19. A method according to  claim 16  wherein the temperature of blood upstream of the heat exchanger is the temperature of blood flowing through the vessel in which the heat exchanger is positioned, taken at a location upstream of the heat exchanger. 
     
     
       20. A method according to  claim 16  wherein the temperature of blood upstream of the heat exchanger is the temperature of blood flowing through a vessel other than the vessel in which the heat exchanger is positioned. 
     
     
       21. A method for determining blood flow rate in a mammalian patient and for heating or cooling at least a portion of the patient's body, said method comprising the steps of:
 A) providing a catheter having a beat exchange device that is useable to change the temperature of at least a portion of the patient's body; 
 B) inserting the heat exchange catheter into the vasculature of the patient and positioning the heat exchanger within a blood vessel; 
 C) causing heat to be exchanged between the heat exchanger and blood flowing past the heat exchanger so as to bring about a change in the temperature of all or a portion of the patient's body; 
 D) determining the amount of heat exchanged between the heat exchanger and the blood within a time period; 
 E) determining the temperature of blood flowing through the blood vessel upstream of the heat exchanger; 
 F) determining the temperature of blood flowing through the blood vessel downstream of the heat exchanger; and, 
 G) determining the flow rate of blood in the vessel based on the amount of heat exchanged between the heat exchanger and the blood and the difference between the temperature of blood upstream of the heat exchanger and the temperature of blood downstream of the heat exchanger; 
 the amount of heat exchanged between the heat exchanger and the blood in Step D being determined by the formula:
     q=m ·( t   in   −t   out ) K  
 
 
 wherein q=heat exchange, m=flow rate of heat exchange fluid through the heat exchanger, t in =temperature of heat exchange fluid entering the heat exchanger, t out =temperature of heat exchange fluid exiting the heat exchanger and K=the thermal constant of the heat exchanger fluid. 
 
     
     
       22. A method according to  claim 21  wherein the flow rate of blood through the vessel is determined in Step G by the formula:
   Flow Rate per Time Period=Heat Exchanged÷Δ t  
 
 wherein Heat Exchanged=the amount of heat added to or removed from the blood per unit time and Δt=the difference between the temperature of the patient's blood before it undergoes heat exchange with the heat exchanger as measured by a second temperature measuring device and the temperature of blood flowing after it undergoes heat exchange the heat exchanger through the patient's pulmonary artery as measured by a first temperature measuring device. 
 
     
     
       23. A method for determining blood flow rate in a mammalian patient and for heating or cooling at least a portion of the patient's body, said method comprising the steps of:
 A) providing a catheter having a heat exchange device that is useable to change the temperature of at least a portion of the patient's body; 
 B) inserting the heat exchange catheter into the vasculature and positioning the heat exchanger within a blood vessel; 
 C) causing heat to be exchanged between the heat exchanger and blood flowing past the heat exchanger so as to bring about a change in the temperature of all or a portion of the patient's body; 
 D) determining the amount of heat exchanged between the heat exchanger and the blood within a time period; 
 E) determining the temperature of blood flowing through the blood vessel upstream of the heat exchanger; 
 F) determining the temperature of blood flowing through the blood vessel downstream of the heat exchanger; and, 
 G) determining the flow rate of blood in the vessel based on the amount of heat exchanged between the heat exchanger and the blood and the difference between the temperature of blood upstream of the heat exchanger and the temperature of blood downstream of the heat exchanger, the flow rate of blood through the vessel being determined by the formula:
   Flow Rate per Time Period=Heat Exchanged÷Δ t  
 
 
 wherein Heat Exchanged=the amount of heat added to or removed from the blood per unit time and Δt=the difference between the temperature of the patient's blood before it undergoes heat exchange with the heat exchanger as measured by a second temperature measuring device and the temperature of blood flowing through the patient's pulmonary artery as measured by a first temperature measuring device. 
 
     
     
       24. A method according to  claim 23  wherein the amount of heat exchanged between the heat exchanger and the blood is determined in Step D by the formula:
     q=m ·( t   in   −t   out ) K  
 
 wherein q=heat exchange, m=flow rate of heat exchange fluid through the heat exchanger, t in =temperature of heat exchange fluid entering the heat exchanger, t out =temperature of heat exchange fluid exiting the heat exchanger and K=the thermal constant of the heat exchanger fluid. 
 
     
     
       25. A method for determining cardiac output or discerning a substantial change in cardiac output in a mammalian patient, the method comprising the steps of:
 A) providing a heat exchange catheter that comprises an elongate catheter body having a heat exchanger positioned thereon; 
 B) inserting the heat exchange catheter into the vasculature and positioning the heat exchanger within a blood vessel through which the blood flow rate is substantially the same as or bears a known relationship to cardiac output in that the luminal diameter of the vessel is estimated based on the height and weight of the patient; 
 C) causing heat to be exchanged between the heat exchanger and blood flowing past the heat exchanger; 
 D) determining the amount of heat exchanged between the heat exchanger and the blood within a time period; 
 E) determining the flow rate of blood past the heat exchanger based on the amount of heat exchanged in the time period; and, 
 F) computing at least an estimate of cardiac output or discerning a change in cardiac output, on the basis of the flow rate determined in Step E, 
 wherein the luminal diameter of the vessel in which the heat exchanger is positioned is estimated based on the height and weight of the patient. 
 
     
     
       26. A method according to  claim 25  wherein Step C is carried out such that the amount of heat exchanged between the heat exchanger and the blood results in a change in the temperature of all or part of a patient's body so as to induce hypothermia, induce hyperthermia, maintain normothermia or achieve and maintain a temperature that is different from that patient's normothermic temperature. 
     
     
       27. A method according to  claim 25  wherein the flow rate of blood is determined in Step E by reference to a database which correlates flow rate values to corresponding amounts of heat exchange measured in Step D for blood in vessels having different luminal diameters. 
     
     
       28. A method according to  claim 25  wherein the flow rate of blood is determined in Step E by the following formula:
     CO =Heat Exchanged÷Δ t  
 
 wherein CO=the amount of blood passing through the right heart per unit time, Heat Exchanged=the amount of heat added to or removed from the blood per unit time and Δt=the difference between the temperature of the patient's blood before it undergoes heat exchange with the heat exchanger and the temperature of blood
     CO =Heat Exchanged÷Δ t  
 
 
 wherein CO=the amount of blood passing through the right heart per unit time, Heat Exchanged=the amount of heat added to or removed from the blood per unit time and Δt=the difference between the temperature of the patient's blood before it undergoes heat exchange with the heat exchanger and the temperature of blood flowing after it undergoes heat exchange with the heat exchanger. 
 
     
     
       29. A method according to  claim 25  wherein the heat exchanger is positioned in the venous vasculature and wherein a computed or estimated cardiac output is calculated in Step F by multiplying the flow rate determined in Step E by a factor representing the portion of total venous blood flow through the right heart that comes from the vessel in which the heat exchanger is positioned. 
     
     
       30. A method for determining cardiac output or discerning a substantial change in cardiac output in a mammalian patient, the method comprising the steps of:
 A) providing a heat exchange catheter that comprises an elongate catheter body having a heat exchanger positioned thereon; 
 B) inserting the heat exchange catheter into the vasculature and positioning the heat exchanger within a blood vessel through which the blood flow rate is substantially the same as or bears a known relationship to cardiac output; 
 C) causing heat to be exchanged between the heat exchanger and blood flowing past the heat exchanger; 
 D) determining the amount of heat exchanged between the heat exchanger and the blood within a time period; 
 E) determining the flow rate of blood past the heat exchanger based on the amount of heat exchanged in the time period; 
 F) computing at least an estimate of cardiac output or discerning a change in cardiac output, on the basis of the flow rate determined in Step E; and 
 G) measuring the luminal diameter of the vessel in which the heat exchanger is positioned. 
 
     
     
       31. A method according to  claim 30  wherein the luminal diameter of the vessel in which the heat exchanger is positioned is measured on an image of the vessel obtained by an imaging technique selected from the group consisting of:
 fluoroscopy; 
 ultrasound imaging; 
 intravascular ultrasound imaging; 
 magnetic resonance imaging; 
 computed tomographic imaging; 
 angiography; and, 
 X-ray. 
 
     
     
       32. A method according to  claim 30  wherein Step C is carried out such that the amount of heat exchanged between the heat exchanger and the blood results in a change in the temperature of all or part of a patient's body so as to induce hypothermia, induce hyperthermia, maintain normothermia or achieve and maintain a temperature that is different from that patient's normothermic temperature. 
     
     
       33. A method for determining cardiac output or discerning a substantial change in cardiac output in a mammalian patient, the method comprising the steps of:
 A) providing a heat exchange catheter that comprises an elongate catheter body having a heat exchanger positioned thereon; 
 B) inserting the heat exchange catheter into the venous vasculature and positioning the heat exchanger within a blood vessel through which the blood flow rate is substantially the same as or bears a known relationship to cardiac output; 
 C) causing heat to be exchanged between the heat exchanger and blood flowing past the heat exchanger; 
 D) determining the amount of heat exchanged between the heat exchanger and the blood within a time period; 
 E) determining the flow rate of blood past the heat exchanger based on the amount of heat exchanged in the time period; and, 
 F) computing at least an estimate of cardiac output by multiplying the flow rate determined in Step E by a factor representing the portion of total venous blood flow through the heart that comes from the vessel in which the heat exchanger is positioned, or discerning a change in cardiac output, on the basis of the flow rate determined in Step E. 
 
     
     
       34. A method according to  claim 33  wherein at least a portion of the heat exchanger is positioned in the inferior vena cava and the factor applied for that portion of the heat exchanger is approximately ⅔. 
     
     
       35. A method according to  claim 33  wherein at least a portion of the heat exchanger is positioned in the inferior vena cava and the factor applied for that portion of the heat exchanger is approximately ⅓. 
     
     
       36. A method according to  claim 33  wherein at least a portion of the heat exchanger is positioned in the right atrium and the factor applied for that portion of the heat exchanger is 100%. 
     
     
       37. A method for determining cardiac output or discerning a substantial change in cardiac output in a mammalian patient, the method comprising the steps of:
 A) providing a heat exchange catheter that comprises an elongate catheter body having a heat exchanger through which a heat exchange fluid is circulated, positioned thereon; 
 B) inserting the heat exchange catheter into the vasculature and positioning the heat exchanger within a blood vessel through which the blood flow rate is substantially the same as or bears a known relationship to cardiac output; 
 C) causing heat to be exchanged between the heat exchanger and blood flowing past the heat exchanger; 
 D) determining the amount of heat exchanged between the heat exchanger and the blood within a time period, the amount of heat exchanged being calculated based on the amount of power consumed by an external unit; 
 E) determining the flow rate of blood past the heat exchanger based on the amount of heat exchanged in the time period; and 
 F) computing at least an estimate of cardiac output or discerning a change in cardiac output, on the basis of the flow rate determined in Step E. 
 
     
     
       38. A method according to  claim 37  wherein the amount of heat exchanged between the heat exchanger and the blood is determined by the formula:
     q=m ·( t   in   −t   out ) K  
 
 wherein q=heat exchange, m=flow rate of heat exchange fluid through the heat exchanger, t in =temperature of heat exchange fluid entering the heat exchanger, t out =temperature of heat exchange fluid exiting the heat exchanger and K=the thermal constant of the heat exchanger fluid. 
 
     
     
       39. A method for determining cardiac output or discerning a substantial change in cardiac output in a mammalian patient, the method comprising the steps of:
 A) providing a heat exchange catheter that comprises an elongate catheter body having a heat exchanger positioned thereon; 
 B) inserting the heat exchange catheter into the vasculature and positioning the heat exchanger within a blood vessel through which the blood flow rate is substantially the same as or bears a known relationship to cardiac output; 
 C) causing heat to be exchanged between the heat exchanger and blood flowing past the heat exchanger; 
 D) determining the amount of heat exchanged between the heat exchanger and the blood within a time period; 
 E) determining the flow rate of blood past the heat exchanger based on the amount of heat exchanged in the time period; 
 F) computing at least an estimate of cardiac output or discerning a change in cardiac output, on the basis of the flow rate determined in Step E; 
 G) measuring the temperature of blood downstream of the heat exchanger; and 
 H) measuring the temperature of blood upstream of the heat exchanger; 
 wherein the amount of heat exchanged in the time period is determined in Step D by the formula:
   downstream temperature−upstream temperature.
 
 
 
     
     
       40. A method according to  claim 39  wherein the temperature of blood downstream of the heat exchanger is measured in the pulmonary artery. 
     
     
       41. A method according to  claim 39  wherein the temperature of blood upstream of the heat exchanger is the temperature of blood flowing through the vessel in which the heat exchanger is positioned, taken at a location upstream of the heat exchanger. 
     
     
       42. A method according to  claim 39  wherein the temperature of blood upstream of the heat exchanger is the temperature of blood flowing through a vessel other than the vessel in which the heat exchanger is positioned. 
     
     
       43. A method according to  claim 39  wherein the temperature of blood upstream of the heat exchanger is taken as the temperature of the patient's body taken at an extravascular location.